1. Technical Field
The present disclosure relates to a three-dimensional (3D) stereoscopic image rendering (i.e., creating and projecting) system; more specifically, it is related to such a system that utilizes a lenticular lens sheet and suppresses moiré patterns.
2. Description
In recent years, three-dimensional (3D) graphical rendering devices (note, we use the term “rendering” to refer variously to the creation, presentation, display and projection of images) have received wide attention from the consumer. Products employing 3D rendering, such as gaming devices, mechanical drafting programs and medical image rendering devices, have been developed by various companies. Among the many technologies used in the implementation of these devices, the lenticular lens (or sheets of such lenses) is considered to be one of the most mature, and products using lenticular lenses can be found in flat panel televisions, notebook computers, smartphones and game consoles. Compared to the other types of 3D stereoscopic image rendering devices, the device using a lenticular lens, or more generally a sheet of such lenses, formed as a multiplicity of parallel, contiguous individual lenticular lenses, outperforms its peers mainly by its user-friendliness. Specifically, it produces a 3D stereoscopic image that is projected directly to the naked eye.
The human brain can compare the images captured by the left eye and the right eye and transmit depth data obtained from comparison of the two images to other areas of the brain where, among other things, they produce the 3D effect. Without the use of additional devices such as eyeglasses, a lenticular lens-based 3D displaying device automatically projects two different images of even a 2D object, one to the viewer's left eye and one to the viewer's right eye, for efficient use by the brain in creating a 3D effect. This unique characteristic makes a lenticular lens sheet a promising product in the next generation 3D display market.
Despite its functional advantage of naked eye viewing, the conventional lenticular lens has a fundamental drawback related to optical effects associated with its cylindrical columnar construction. Specifically, as will be described below, the conventional lenticular lens sheet can “dissipate” stray light along the lens column (hereinafter denoted as the longitudinal or Y-direction) relatively easily, in a manner analogous to the propagation of a light wave in glass fiber. Whenever there is stray light traveling in the longitudinal direction within the lens, because of the small diameter (e.g., less than 1.0 mm) and the elongated length of the lens column (e.g., tens of cm), the intensity of this stray light will be reduced by the averaging effects of multiple internal reflection processes. If typically viewed from a position perpendicular to the plane of the displaying device, the desired 3D stereoscopic image would be seen as being blended with a dim background light. The intensity of this background light is so low that it is almost undiscernible to the human eye. In reality, this background light comes from the stray light that “leaked out” of the interior of the lenticular lens column, through its surface, as the result of multiple internal reflections from the interior of that surface. Since these background light rays do not carry any image pattern, they will generally not bother a viewer. However, if there is a periodic pattern characterizing the image-producing layer that lies beneath and supports the lenticular lens sheet, the image-producing layer typically being a black, or less reflective matrix surrounding light-emitting subpixels, a vague pattern may also appear in the blended image. This is the combination of the primary 3D stereoscopic image produced by the lens sheet and the background image produced by the interaction of the stray light with the black matrix surrounding the subpixels. As a result, the problem denoted “moiré patterns” is created. To overcome this moiré problem, the conventional art has devised various means to “shunt” the occasional crossing-over between the black matrix and the lenticular lens. Van Berkel et al., (U.S. Pat. No. 6,064,424) shows one such method where the lenticular lens is placed on a displaying panel in a relatively slanted manner (denoted by the slanting angle α). Alternatively, van Berkel (U.S. Pat. No. 6,801,243) also discloses a special means of addressing the subpixels of a 3D stereoscopic image rendering device using a lenticular lens. Still further, Sekine, (U.S. Pat. No. 8,823,890) discloses a black matrix with a specific value of its width for the sake of suppressing moiré patterns. Other approaches are also taught by Coleman (U.S. Pat. No. 8,408,775) and by Kim et al. (U.S. Pat. No. 8,928,222).
Although prior art has progressed to some degree in suppressing the moiré problem, as of yet there has been no pervasive technological solution disclosed or universally adopted. For example, the prior art approach that slanted the lenticular lens column to “shunt” the encounter with the black matrix which was deemed to be the source of moiré images, may alleviate the moiré problem to some extent in that it lowers the number of the black stripes composing the black matrix that are being overlapped by the lenticular lens sheet. But the moiré problem cannot be totally cured by this prior art approach; whenever the contrast of an image is relatively high, or the total illuminance of an image is relatively high, the viewer may still occasionally observe a moiré image.
Fundamentally, the above cited prior arts are all inadequate approaches that try to suppress the impact of the stray light rays within the lenticular lens. Their inadequacies are because the light rays that really cause the moiré problem still exist. By failing to address the moiré problem from an optical engineering point of view, the prior art was merely “covering up” the problem. What is worse, after slanting the lenticular lens, the prior art that did so is then required to do the additional development work on the driving circuitry of the displaying device (e.g., liquid crystal display (LCD), organic light-emitting diode (OLED), etc.); so, the cost of manufacturing is increased. Still further, when the form factor of a displaying device is inevitably changed, as the displaying device industry is an constantly evolving industry, this prior art approach would have to devise another new type of lenticular lens sheet (e.g., differing in slant angle, pitch, radius of curvature, etc.) plus another new driver program for the image-producing layer, to meet the ever-changing engineering specifications.
Fundamentally, the state-of-the-art lenticular lens device needs a comprehensive method that addresses the moiré problem from an optical engineering perspective, i.e., a method that is based upon the fundamentals of lens design, or the effects of internal reflection. That will be the goal of the present disclosure.